Xerographic fixing apparatus



Feb. 26, 1963 J. .1. CODICHINI ETAL 3,07

XEROGRAPHIC FIXING APPARATUS 3 Sheets-Sheet 1 Filed Jan. 2, 1962 lNl EN TORS J. CODICHINI A TTOR/VEV Feb. 26, 1963 J. J. CODICHINI ETAL 3,079,483

XEROGRAPHIC FIXING APPARATUS Filed Jan. 2, 1962 3 Sheets-Sheet 2 XJIIIIIIlrII I III]! II ATTORNEK 1963 J. J. CODlCHlNl ETAL 3,07

XEROGRAPHIC FIXING APPARATUS 3 Sheets-Sheet 3 Filed Jan. 2, 1962 m6 Twit ATTORNEY United rates Patient O 3,97%,483 XEROGRAPHEQ FiXiNG APPARATUS Joseph J. Codichini and Rolf W. Eiclrier, Fairport, William G. Lewis and Karl A. Northrup, Rochester, Robert F. Osborne, Webster, and John J. Schoen, Rochester,

N.Y., assignors to Xerox Corporation, Rochester, Nfifl,

a corporaton of New York Filed Jan. 2, 1962, Ser. No. 163,473

2 Claims. (Ql. 2l919) This invention relates to improvements in heat fusers and, particularly, to an improved apparatus for heat fixing of xerographic powder images.

More specifically, the invention relates to an improved heat fuser for use in the field of xerography to fuse resinous powder images on a support material.

In the process of xerography, for example, as disclosed in Carlson Patent 2,297,691, issued October 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them and thereby creates an electrostatic latentimage on or in the photoconducive layer. Development of the latent image is effected with an clectrostatically charged, finely divided developing material or toner which is brought into surface contact with the photocondu ctive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xcrographic powder image is usually transferred to a support surface such as paper to which it may be fixed by any suitable means.

One of the methods in common use for developing the electrostatic latent image is described in Walkup Patent 2,618,551 and is known as cascade development, and is in general use for line copy development. in this tech nique, the powder or toner is mixed with a granular fcarrier material, and this two-component developer is poured or cascaded over the plate surface. The function of the carrier material is to improve the flow characteristics of the powder and to produce, on the powder, by triboelectrification, the proper electrical charge so that'the powder will be attracted to the image. More exactly, the function of the carrier material is to provide the mechanical control to the powder, or to carry the powder to an image surface and, simultaneously, to providehomogeneity of charge polarity.

, In the Carlson patent it is noted that a variety of types of finely divided electroscopic powders may be employed fioi developing electrostatic latent images. However, as the art of'xerography has progressed, it has been found preferable to develop line copy images with a powder or toner formed of any of a variety of pigmented thermoplastic resins that. have been specifically developed for the. purpose. A number of such developing materials are manufactured and marketed by Xerox Corporation of Rochester, New York, and are specifically compounded for producing dense images of high resolution and to have characteristics to permit convenient storage and handling. Such developing materials are compounded to permit them to be fixed to the surface of a transfer material either by heat fixing or vapor fixing techniques, in accordance with the particular application in which they are employed; that is, the individual particles of resin (toner) soften and coalesce when heated or plasticized by solvent, so that they become sticky and readily adhere to the surface of the transfer material.

One of the important applications of the process of xerography comprises its use in automatic copying ma- 3,079,483 Patented F eb. 26, 1963 EQQ chines for general office use wherein the powder images formed on a xerographic plate are transferred to cut sheet paper and then fixed thereon by heat fusing. In order to fuse resinous powder images formed of the powdered resins now commonly used, it is necessary to heat the powder and the paper to which it is to be fused to a relatively high temperature, such as approximately 325 F. It is undesirable, however, to raise the temperature of the paper substantially higher than 375 F.because of the tendency of paper to discolor at such elevated temperatures. 1 v

This imposes rather exacting temperature control requirements on the fusing device and also makes it necessary that the heat be distributed uniformly over the surface area of the support material to be treated. A further requirement is that no portion of the support material should accidentally come into contact with the heating element, or if it comes into contact with the heating element, the heating element shall have a temperature that will not damage the support material.

Other requirements are that the heat fuser shall provide good and rapid heat transfer to the sheet of support material being treated, and that it shall have relatively low power consumption when left on for extended periods of time, such as when it is maintained in stand-by condition, and that heat dissipation from the heat fuser shall be kept at a minimum to prevent possible damage to the xerographic plate reproducing apparatus.

It is therefore an object of this invention to improve heat fusing apparatus to satisfy the above-stated fusing requirements.

Another object of this invention is to improve heat fusers to provide uniform heating of a support material carrying a fusible power image thereon.

It is a further object of the invention to improve xerographic fixing apparatus for fusing large surface areas of a support material and to accomplish the fixing free from danger of charring or other damage to the support material.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 illustrates schematically an automatic xerographic reproducing apparatus using a preferred embodiment of the heat fuser of the invention;

FIG. 2 is a left-hand side view of a preferred embodiment of a heat fuser constructed in accordance with the invention;

PKG. 3 is a top view of the heat fuser with parts broken away;

FIG. 4 is a front view, in terms of the direction of paper travel, of the heat fuser; and,

7 FIG. 5 is a sectional view of the heat fuser taken along line 5-5 of FIG. 3.

General As shown, the xerographic apparatus comprises a xerographic plate including a photoconductive layer or light receiving surface on a conductive backing and formed in the shape of a drum, generally designated by numeral 20, which is journaled in a frame to rotate in the direction indicated by the arrow to cause the drum surface sequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographic processing stations in the path of movement of the drum surface may be described functionally,as follows:

A charging station, at which a uniform electrostatic charge is deposited on the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern ofcopy to be reproduced is projected on to the drum surface to dissipate the drum charge in the exposed areas thereof and thereby form a latent electrostatic image of the copy to be reproduced;

A deyeloping station, at which a xerographic developing material including toner particles having an electrostatic charge opposite to that of the electrostatic latent image are cascaded over the drum surface, whereby the toner particles adhere to the electrostatic latent image to form a xerographic powder image in the configuration of the copy to be reproduced;

A transfer station, at which the xerographic powder image is electro-statically transferred from the drum surface to a transfer material or support surface; and,

A drum cleaning station, at which the drum surface is first charged and then brushed or wiped to remove residual toner particlesrem-aining thereon after image transfer, and at which the drum surface is exposed to a relatively bright light source to effect substantially complete discharge of any residual electrostatic charge remaining thereon.

Thecharging station is preferably located as indicated by reference'charaoter A in the schematic illustration of the apparatus. In general, the Charging apparatus or corona charge device 21 includes a corona discharge array of one or more discharge electrodes that extend transversely across the drum surface and are energized from a. high potential source and are substantially enclosed within a shielding member.

Next sub-sequent thereto in the path of motion of the xerographic drum is an exposure station B. This exposure station may be one of a number of types of mechanisms or members such as-desirably an optical scanning or projection system, or the like, designed to project a line copy image onto the surface of the photoconductive xerographic drum from a suitable original. The optical scanning or projection assembly consists of a copyboard in the shape of a drum, hereinafter referred to as copy drum 30, which is adapted to support copy to be reproduced and arranged to rotate in light-projection relation to the moving light-receiving surface of the xerographic plate. Uniform lighting is provided by suitable lamps Slattached to a slotted light reflector 32 mounted adjaceneto the copy drum.

A- slotted-light shield 33, adapted to protect the xerographic plate fro-m extraneous light, is positioned adjacent to the surface of the xerographic plate. A slot aper turein the light shield extends transversely to the path ofmovement of the light-receiving surface of the xerographic drum 20 to permit reflected rays from the copy drum to be directed against a limited transverse area of the light-receiving surface as it passes thereunder.

To enable the optical system to be enclosed within a relatively small cabinet, a folded optical system including an object mirror 34, a lens 35, and an image mirror 36, is used in the preferred embodiment of the apparatus.

A document fed through document guides 37 to the copy drum is removably secured'thereon by a suitable gripper mechanism for movement therewith in timed relation to the movement of the xerographic drum whereby a flowing image of the copy is projected onto the xerographic drum. The copy isheld against the surface of thecopy drum until gripped by meansof document retaining guides 38. Pressure guides 39 and document guard 41 retain and gdiide the trailing edge of the document on the. copy drum. After the copy is scanned it is released from the copy drum to be transported out of the machine by the copy drum and document feed out rollers through document feed out guide 43.

Adjacent to the exposure station is a developing station C in which there is positioned a developer apparatus 50 including a developer housing having a lower or sump portion for accumulating developer material 51. Mounted within the developer housing is a driven bucket-type conveyor 52 used to carry the developer material previously supplied to the developer housing to the upper portion of the developer housing from where the developer material is cascaded over a hopper chute 53 onto the drum.

As the developer material cascades over the drum, toner particles of the developer material adhere electrostatically to the previously formed electrostatic latentimage areas on the drum to form a visible x-erographicpowder image; the remaining developer material falling off the peripheral surface of the drum into the bottom of the developer housing. Toner particles consumed during the developing operation to form the xerographic powder images are replenished by a toner dispenser 54, of the type disclosed in copending application Serial No. 776,976, filed November 28, 1958, in the name of Robert A. Hunt, mounted within the developer housing.

Positioned next ad acent to the developing'station is the image transfer station D which includes suitable sheet feeding mechanism adapted to feed sheets of paper successively to the xerographic drum in coordination with the presentation of the developed image on the drum at the transfer station. The sheet feeding mechanism in: cludes a sheet source such aspaper tray 60 for a plurality of sheets of a, suitable support material, that is, sheets of paper or the like, separator rollers 61 adapted to feedthe top sheet of the stack of support material through aguide 67 to a sheet conveyor mechanism 62 having paper grippers 6,3 thereon which carry the sheet supportinaterial into contact with the rotating'xerographic drunrin coordination with the appearance of a developed jimageat the transfer station.

The transfer of the xerographic, powder image from the drum surface to the support material is .elfected'by means of a corona transfer device 64that is located at" or immediately after the point of contact between the.

support material and the rotating Xerographic drum. The

corona transfer device 64 is substantially similar to the corona discharge device that is employed at the charging station in that it also includes an array of oneor more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially, enclosed with a shielding member. In operation, the electrostatic field created by the corona transfer device is-effective to tack the transfer material electrostatically to the drum surface and simultaneously with the tacking action, the

electrostatic field is effective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the support material.

As the paper gripper mechanism continues to move forward in its closed circuit, it will strip the support material from the xerographic drum and carry it to a fixing device, such as, for example, heat fuser 7t), whereat the developed and transferred xerographic powder image on the support material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point for collection externally of the apparatus. To accomplish this there is provided a pair of delivery rolls 65 and 66'by means of which the copy is delivered from the machine after it is released by the gripper mechanism. Suitable carnmeans 68 and 69 are provided at the receiving and delivery stations of the conveyor mechanism, respectively, to actuate the paper grippers at these stations to receive or discharge a sheet of support material.

The next and final station in the deviceis a drum, cleaning station Ewhereat any powder remaining on the xerographic drum after the transfer step is removed'and whereat the xerographic drum is flooded with lightto cause dissipation of any residual electricalcharge remaining on the xerographic drum.

T o aid in the removal of any residual powder remain; ing on the xerographic drum there isprovided a corona precleaning device 84 that is substantially similar to the.

corona discharge device that is employed at charging station A. Removal of residual'powder from the xerographic drum is effected by means of a web cleaner device 80 adapted to continuously feed a clean fibrous web material into wiping contact with the xerographic drum. As shown, the web material 55 is taken from asupply roll 81 and transported around a cleaning or pressure roll 82, preferably made of rubber, onto a take-up or rewind roll 83'.

Any residual electrical charge remaining on the xerographicdrum is dissipated by light from a fluorescent lamp 85 mounted in a suitable bracket above the xerographic drum, a suitable starter and ballast being provided for energizing the fluorescent lamp.

Suitable drive'means drive the xerographic drum, the copy drum, the sheet conveyor mechanism at predetermined speeds relative to each other, and to effect operation of the :paper separator roll, and the web cleaner mcchanism, the latter being driven at a speed or speeds whereby relative movement between the xerographic drum and the web material is effected. Suitable drive means are also provided for effecting operation of the conveyor mechanism and toner dispenser of the developing apparatus assembly. w

It is believed that the foregoing'description is suffieieut'forthe purpose of this application to show the general operation of a xerographic reproducing apparatus; For further details concerning the specific construction of the'xerographic apparatus shown,-reference is-made .to copending application .Serialfi-No. 162,779, filed concurrently herewithonIDecember 28, 1961, in the name-of Roger? H. Eichorn et a1. j

Fuser The. developing material used to;form the powder imagesare specifically chosen to permit them to be fixed to the support material either by heat-fixing or vapor fixing techniques, that is, the individual particles of resin (toner) soften and coalesce when heated,- or plasticized hy-solvent, so that they become sticky and readily adhere to the support material. Referring now in particular to FIGS. 2 through 5, inclusive, there is shown'a preferred embodiment of a heat fuser 70 constructed in accordance with the invention; 3

The-heat fuser 70 includes a bottom radiant heating panel 501 and a top radiant heating panel 521 mounted ina bottom housing 562 and a top housing 522, respectively, positioned in the machine by frame plates and 1.1, which may be frame plates of the xerographic apparatus, as shown, in spaced apart relation to each other to permit a sheet of support material, carrying an unfused powder image thereon, to be transported between the radiant heating panels for the purpose of heat fixing the powder image onto the support material.

The bottom housing 502 includes a base plate 503 having formed-integrally therewith side walls 5&4 extending along the length of the base plate, end wall 565 and end portions'5tl6 along the'end of the base plate. The bottom housing forms an enclosure for the bottom radiant heating panel 561 which is thermally insulated from the base plate of the housing by' aninsulator 507, such as a mat of fiberglass, positioned between the base plate of the housing'and the radiant heating panel.

The bottom housing is secured to frame plate 11 by means of an angle bracket 508 fastened to the end of portions 506 of the bottom housing and the radiant heating panel, the opposite end of the angle bracket being secured to a support plate 511 supported by pins 518 on frame plate 11. At its opposite end the bottom housing is secured to spacers 512 mounted on angle brackets 513 fastened to a lower support plate 514 secured to frame plate 10.

Strips of insulating material 515 are secured to the bot tom plate by means of a suitable cement material.

Paper guides or supports, such as wire grids 516 are se- 6 cured to opposite ends of the radiant heating panel to extend across the top of the radiant heating panel to prevent a sheet of support material from coming into direct contact with the radiant heating panel.

The top housing 522, similar in construction to the bottom housing, includes a top plate 523 having formed thereon depending side walls 524 extending along the length of the top plate, and depending end walls 525 and end portion 526 extending along the sides'of the plate. The top housing forms an enclosure for the top radiant heating panel 521, thermally insulated from the top plate by an insulator 597 positioned between the top plate and the top radiant heating panel.

The top housing 522 is mounted to frame plate 11 by angle brackets 508 and a support plate 527 in the same manner as the bottom housing 502. At its opposite end, the top housing is secured to spacers 512 mounted on angle brackets 513. Angle brackets 513 are fastened to top support plate 523 secured to frame plate 10. A blanket of insulatitng material 517 is secured to the't'op surface of the top plate 523 by means of'a'suitable cement material. 1 Y l Each radiant heating panel includes a metal-platen 531 formed with circular grooves extending across the length of the platen in substantially parallel relation to each other. Tubular heating elements 532 are secured, as by brazing, in each of the circular grooves.

Each tubular heating element includes a coiled nickelchromium resistance wire 636 compacted in a dielectric material 637 which is enclosed by a metal sheath 638.

The configuration of the resistance wire' 636 of each tubular heating element is such that the individual coils of the wire are more closely spaced at the ends than inthe middle to effect a heating gradient across each unit. By spacing the coils in a predetermined pattern, as described, a uniform temperature distribution is achieved across the face of each radiant heating panel. 1

The metal platen and the exposed portions of the tubular heating elements are coated with a suitable ceramic material, such as ceramic frit, having a minimum emissivity of 0.95.

The tubular heating elements in a panel are connected to each other at one end by a conductor 534 fastened to the terminal pins 533 extending from the metal sheaths, and at the opposite ends the tubular heating elements are connected in pairs to terminal blocks 535 thereby forming unitary resistance elements R1 and R2 for the top and bottom heating panels, respectively, which ar connectable to a source of electrical power.

To conserve heat within the fuser and to limit heat transfer by convection from the heat fuser to the xerographic drum, the opening in the fuser nearest to the xerographic drum is provided with a gate 431 to partly close the opening between the bottom and top radiant heating panels when the fuser is being operated on a stand-by basis. When the xerographi-c apparatus i in operation, the gate is opened to permit a-sheet of support material to be transported to the fuser by the sheet conveyor mechanism. a

The gate 541 secured to a crank rod 542 is pivotally supported by the crank rod journaled in brackets 543 socured to the top radiant heating panel 521. Cutyout portions 544 are provided in the gate for the passage of the endless chains of the sheet conveyor.

In normal operation, the ate is opened by means of a solenoid SOLZ mounted on solenoid bracket 545 secured to the back side of plate 11. A lever 546 is connected at one end by pin 547 to the normally extended armature or plunger of the solenoid and at its other end to the crank rod 542 to actuate the gate. When the solenoid SOLZ is actuated, its plunger is retracted to actuate the crank rod to rotate the gate inward or counterclockwise, as seen in FIG. 2, toward the top radiant heating panel, this movement being in the direction of travel of the sheet conveyor.

by a paper gripper 63 Of the sheet conveyor mechanism 62. Thus, if the. solenoid has failed, the paper gripper,

as it is advanced, will strike the gate to force it open as the sheet gripper travels into the fuser.

In the embodiment shown, the frame plate It) is provided' with a suitable opening through which the fuser assembly is inserted into the machine. To eliminate heat loss from this end of the fuser, a closure plate 551 and aminsulator pad 552 are secured to the bottom and top housings.

Power to the tuser is controlled by means of a conventional thermostat THSl inserted through suitable apertitres i-ninsulating'material 517, top plate 523 and insulator 07,,the thermostat being fastened by a mounting bracket 553 secured to the top radiant heating panel 521.

The radiant heating panels are suitably connected to source of'electric energy, in parallel with each other,

hat inseries, with the thermostat, to permit the thermostat to control the amount of electrical energy supplied tothe radiant. heating panels,

To. guide the trailing edge of a sheet of support material, conveyedthrough the fuser by a paper gripper,

there-is.provided at the front of the fuser, as determined 1 by the direction of travel of the paper gripper, a pair of paper holddown wheels. 561. Each of the. paper holdtlownpwh'eels, in the form of a starwheel, is rotatably 1 mounted; on a pivot-562 securedto a wheel bracket 55-3.

wheel'brackets-5 63. are secured to the top radiant lrcatingpanel 521 to position the paper hold-down wheels fitfl-infront-of the opening into the heat iuser and slightlfy; above the-papergrippers of the sheet conveyor as they advance towapd the fuser. By; using two radiant heating panels mounted face to face with eachother, uniform heating of both sides of f P 16 supportmaterial to facilitate rapid fusing of the pow- 1 derimage carried thereby is obtained and, furthermore,

the useof the radiant steel panels provides uniform heating of the entire surface area of the support material.

While: the invention hasbcen described herein, it is not-confinedto the details set forth, since it is apparent, fprtexample, that the gate could be loosely hinged whereby the only, actuating force on the gate to open it could bethe sheet gripper carried by the sheet conveyor.

- Therefore, this application is intended to cover such modifications or changes as may come within the purpose of the-improvements orthe scope of the following claims.

What is claimed is: 1; Apparatus for fixing a heat fusible powder image to the;surface of a support material,

said: apparatus including an endless sheet conveyor mechanism having at least one sheet gripper secured thereomfor transporting a sheet of support material iniarclosed path from a sheet receiving station to a sheet deliverystation,

a first radiant heating panel and .a second radiant heating" panel positioned between said sheet receiving station'andsaid sheet delivery station in spaced rela- 7 tion to each other to form a chamber thcrebetween through which said sheet gripper of said endless sheet conveyor mechanism transports support material,

eachi-of said radiant heating panels including a metal platen 'having tubular heating elements secured thereon whereby said tubular heating elements are in face'to face relation with each other,

said tubular heating elements being adapted to be con-;

nected to a source of electrical power,

a gate operatively connected to said first radiant heating panel for movement from a first position'in whichsaid gate extends substantially from said first radiant heating panel to said second radiant heating panelto form a movable end wallof said chamber,

to a second position in which said gate is positioned away from said second radiant heating panel,

the direction of movement of said gate to saidsecond position being in the direction: of movement of said sheet gripper through said chamber whereby said sheet gripper is. adapted to open said gate,

and sheet hold-down means mounted on said firstra'-- diant heating panel in position to guide the trailing edge of support material out of contact with said-- gate and said metal. platen and said tubular heating,

elements of said-first radiantheatingpanel. 2. Apparatusfor fixing a heat fusible powder image'- to the surfaceof a support material,.

said apparatus including an endless sheet conveyor: mechanism, havingatleast one sheet gripper secured thereon for transporting}. asheet of support materialin a closed path from a sheet receiving.;stationto a sheet: delivery station,.

a first radiantheating panel" and azsecond'radiant heat ing panelpositioned between saidsheet} receiving station and said sheet delivery station in. spaced relation to each other to form a chamber th'erebetween; through which. saidsheetigripperof ,saitlxendlessisheet conveyor mechanism transports: support material,

each of said radiant heatin'g zpanels including a metal platen having tubular heating elements secured thereon to form a unitary electrical resistance heating ele ment thereon, said metal pla tens=being positioned-in the respective heating panels with; the-tubular heat ing elements of said heating'pa'nels" facing'e'ach other, said tubular heating elementsbeingadaptedto be -'c 'on' nected to a'sourceof electrical-power, a gate operatively'connected to said first radiant heat ing panel for movement from-a first position in which said gate extends substantially from said 'first radiant heating panel to said second' radi'ant heatingpanel References Cited in thefile of this patent UNITED STATES PATENTS 1,550,422 Braemer Aug. 18', 19 28 2,232,926 Bates May 12', 1942 2,564,706 Mochel Aug; 21', ,1951 2,571,218 Del Buttero O ct. 16, 1951 2,807,704 Allen et a1 Sept. 24, 1957 Crumrine Sept. 16, 1958 

1. APPARATUS FOR FIXING A HEAT FUSIBLE POWER IMAGE TO THE SURFACE OF A SUPPORT MATERIAL SAID APPARATUS INCLUDING AN ENDLESS SHEET CONVEYOR MECHANISM HAVING AT LEAST ONE SHEET GRIPPER SECURED THEREON FOR TRANSPORTING A SHEET OF SUPPORT MATERIAL IN A CLOSED PATH FROM A SHEET RECEIVING STATION TO A SHEET DELIVERY STATION, A FIRST RADIANT HEATING PANEL AND A SECOND RADIANT HEATING PANEL POSITIONED BETWEEN SAID SHEET RECEIVING STATION AND SAID SHEET DELIVERY STATION IN SPACED RELATION TO EACH OTHER TO FORM A CHAMBER THEREBETWEEN THROUGH WHICH SAID SHEET GRIPPER OF SAID ENDLESS SHEET CONVEYOR MECHANISM TRANSPORTS SUPPORT MATERIAL, EACH OF SAID RADIANT HEATING ELEMENTS SECURED THEREON WHEREBY SAID TUBULAR HEATING ELEMENTS ARE IN FACE TO FACE RELATIN WITH EACH OTHER SAID TUBULAR HEATING ELEMENTS BEING ADAPTED TO BE CONNECTED TO A SOURCE OF ELECTRICAL POWER, A GATE OPERATIVELY CONNECTED TO SAID FIRST RADIANT HEATING PANEL FOR MOVEMENT FROM A FIRST POSITION IN WHICH SAID GATE EXTENDS SUBSTANTIALLY FROM SAID FIRST RADIANT 